I think we all appreciate the significance/implications of the last two annmnts on the matrix permeability and porosity, and thermal maturity.
But how many UNDERSTAND them and can connect the dots to the potential for overpressure and effective flow rates.
Here's an attempt to explain it with the dual aim of clarifying these issues in my mind and passing on this knowledge as well.
After all KNOWLEDGE is power.
Firstly we need some definitions.
POROSITY: Pores, voids or free space within the rock.
PERMEABILITY: The ability of fluids and/or gases to pass between the rock pores. Or, if you like, the interconnections between the pores that allow movement of liquids/gases.
Note from the diagram below that you can have good porosity but no permeability because there are no interconnections between the pores.
The MATRIX PERMEABILITY annmnt
http://clients2.weblink.com.au/news/pdf_1\01710487.pdf
stated that:
"permeability within the cored HRZ shale EXCEEDS EXPECTATIONS, several times greater than effective cutoff in all 18 core samples measured.
2 samples displayed permeability too high to be measured using standard technique (indicating possible presence of “permeability super highways”)"
and
"Porosity confirmed at upper end of expectations as per prognosis"
So one would expect that with high porosity the HRZ would have the ability to store relatively high % of fluids. But just as importantly because the HRZ has "upper end" permeability that the HRZ
should have the ability to let fluids move relatively easily through the HRZ strata.
The INTIMATION is made in this annmnt that good flow rates would be possible due to the good permeability:
"Both the permeability and porosity results are at the upper end of expectations and
significantly in excess of the cutoff limits required for the HRZ shale play to be successful."
The annmnt also mentions that light oil and condensates were observed leaching from the cores.
"As previously reported, light oil and condensate was observed leaching from core material, confirming the presence of liquid hydrocarbons at the Icewine#1"
This statement achieves 3 things.
1) That the hydrocarbons appear to move easily from the HRZ cores supporting the good fluid movement.
2) That the thermal maturity appears to be correct due to the presence of both light oil and GAS condensate.
3) That's there is GAS condensate present in the HRZ.
Its history that the second point was confirmed by this annmnt.
http://clients2.weblink.com.au/news/pdf_1\01711732.pdf
"Final Thermal Maturity Analysis Indicates Icewine#1 in Crossover Between Volatile Oil and Condensate Window – Pre Drill Predictions Proven to be Accurate"
"Resultant Low Viscosity Vapour Phase Hydrocarbons Modelled to Flow at Material Rate Given Porosity and Permeability Results"
The point of interest here is that the correct gaseous hydrocarbons (via analysis) confirm the thermal maturity model.
That's the easy bit !!!
We know they have confirmed the correct thermal maturity and consequently the correct light oil and gas condensate must have been present in THOSE BEAKERS !!!
It stands to reason from Basinski's model that these hydrocarbons should flow well through the HRZ as per this statement:
"Resultant Low Viscosity Vapour Phase Hydrocarbons Modelled to Flow at
Material Rate Given Porosity and Permeability Results"
Bit of an underwhelming word that,MATERIAL, imho.
I take it it is being used as an adjective in this phrase. Appropriate synonyms that could have been used are
SIGNIFICANT, MAJOR, IMPORTANT.
This could eventuate as the understatement of the decade in the tight oil industry.
So lets move on to the somewhat more difficult subject of how the Thermal Maturity sweet spot will contribute to good over-pressure, or the ability of the hydrocarbons to move more effectively from the HRZ.
So what is present in a SWEET SPOT with the correct Thermal Maturity.
The Thermal Maturity Sweet Spot will contain what is known as Light or Volatile oil. It will also contain hydrocarbons in the gas phase.
These gaseous hydrocarbons are under immense pressure and high temperatures, both conditions which contribute to the gaseous hydrocarbons retaining a gaseous state within the pore spaces.
This mix of Light tight oil(LTO) and gas is due to the correct % of organic matter being present and exposed to the correct temperatures and pressures during its formation. So correct Thermal Maturity is implied by the correct hydrocarbons being present in a sample at the correct relative percentage.
Successful production of LTO from tight oil formations requires around 15-20% gas within the reservoir pore spaces in order to drive the LTO to the bore hole usually via the fractured shale.
As mentioned the Thermal Maturity annmnt stated that 88E has indeed located the thermal sweet spot at Icewine which from the info above directly intimates the correct gas % being present via hydrocarbon analysis as well as the observation of gas condensate leaching form the core samples.
The gas condenses or changes from its gaseous state to its liquid state (gas condensate) due to the pressure drop on the gaseous hydrocarbons when the core is exposed to the much lower atmospheric pressure and temperatures.
The gaseous hydrocarbons will create a pressure gradient between the pores with which they are contained and the well fractures and any permeability that allows flow between the pores. As the first annmnt stated the permeability of the HRZ EXCEEDED expectations in all core samples and was so high as to be immeasurable in 2 samples.
So we know the LTO should flow very well due to the excellent permeability.
But this high permeability also has another major benefit.
When the hydrocarbon gases condense they can create blockages in the smaller pore throats or lower % of permeability channels due to the hydrocarbon chains being relatively heavy.
However with permeability AND porosity being high at Icewine the chances of this occurring will be much reduced and should contribute to the efficiency of the wells. It has been known for such issues to decrease oil production by 50% once the dew point is reached via the pressure drop when drilling/fracking and a sufficient build up of gas condensate has resulted in serious permeability drop. This would be a problem in Unconventional LTO plays with smaller pores and lower permeability. Yes many of these issues can be solved with proppants but if it is virtually unnecessary to utilize such fluid additives due to having excellent permeability and good porosity this will surely reduce costs of production as well.
So what of OVER-PRESSURE.
As mentioned above at least 15-20% gaseous hydrocarbon is required within the pore spacing (Gas to oil ratio or GOR) to enable the LTO movement out of the pores. Again as implied in the Thermal Maturity annmnt this ratio should be correct given correct thermal maturity data. So we know the gas is present within the pores to drive the LTO to the well fracks and bore hole.
THE FACT THAT THE CORRECT GOR IS PRESENT IS ALSO HIGHLY INDICATIVE that the gas is being retained within the HRZ and therefore THERE SHOULD BE GOOD RETAINING SEALS PRESENT.
As the drilling annmnt stated the well was drilled to below the HRZ in order to analyse the pebble shale below the HRZ and confirm that it creates a good bottom seal. This is another piece of info we will need guidance on in upcoming anncments. Would be a little surprised if its not in the rock mechanics annmnt.
The other variable is the top seal of which I currently have no info apart from this formation description of the strata above the HRZ/HUE from the drilling annmnts.
http://clients2.weblink.com.au/news/pdf_2\01693030.pdf
Drilling recommenced in the 8.5” intermediate hole through the Brookian sequence from 8,773’ on November 29 (AK time). The mid Cretaceous unconformity, a key subsurface marker, was intersected at 9,465’, on prognosis. Geology in the Canning / Seabee Formations (Lower Brookian) has been characterised by predominantly fine grained siltstones and minor unconsolidated sandstones, interbedded with claystones. Multiple minor oil shows and elevated background gas (C1 – C5+) has been encountered throughout the interval.
Whether this geology above the HRZ will create an effective top seal will depend on further rock mechanic data.
d.
(20min delay)